1. Field of the Invention
The present invention relates to linear beam devices, and more particularly, to a resonant cavity arranged to deflect an electron beam.
2. Description of Related Art
Many applications require the deflection of an electron beam. For example, a cathode ray tube includes an evacuated region containing an electron gun that is a source of an electron beam, and a fluorescent screen. When the electron beam strikes the fluorescent screen, light is emitted from the point of impact. The electron beam may be deflected and modulated by the application of electromagnetic fields in such a way that an image is made to appear on the screen.
When deflected at very high frequencies, an electron beam can be used to produce electromagnetic radiation. It is well known in the art to use a resonant cavity to develop an electric field suitable for this purpose. For optimal performance, the cavity should exhibit the following properties: the transit time of the beam through the electric field should be less than half of an radio frequency cycle; the cavity should exhibit a high drive-power-to-deflection conversion efficiency; the beam should be deflected uniformly across the beam profile to maintain beam quality; and the geometry of the cavity should be compact to allow close spacing of multiple cavities, allowing compound deflection profiles.
A conventional solution is a cylindrical pillbox cavity operating in the transverse-electric-field TE111 mode, as illustrated in FIG. 1 (prior art). The TE111 mode cannot be supported in such a cavity if the height of the cavity becomes too small. This limits its application to very high-energy beams with electron velocities great enough to cross the cavity in less than half a cycle. At lower energies, re-entrant drift tube noses are required to limit the transit time, resulting in E-field depression and a considerable reduction in interaction impedance. Accordingly, it would be desirable to provide a linear beam device with a resonant cavity arranged to selectively deflect an electron beam at relatively low energy.